Photovoltaic cell arrays convert solar energy into electricity. In practice, these arrays are configured for connection to an electrical power grid in what are commonly known as solar panels. An individual solar panel can be quite large: while there is no specific standard size, in the United States the vast majority of solar panels for residential use are about 65 inches tall and about 40 inches wide, and for commercial use are about 77 inches tall and about 40 inches wide. Some custom panels are smaller, and many are larger. Furthermore, solar panels are typically connected in panel arrays to take advantage of the available space at installation. Solar panel arrays can be hundreds of feet long.
The conversion efficiency of a solar panel is affected by many factors, including size, number and composition of cells, materials used in electrical connections, installation and configuration parameters, intensity of incident light, and environmental conditions. Dirt, debris, and other deposits can accumulate on the surface of the solar panel, interrupting and degrading the cells' exposure to the sun. The panels must be cleaned, and owners of large installations typically hire solar panel cleaning professionals to handle the project in an experienced manner. Unfortunately, arrays are often so large that cleaning them is risky even for professionals. Installations are often on roofs high above ground, and may be so tall that the cleaner must walk or otherwise put his body weight directly on the panels to reach the entire panel surface. Additionally, the panel surface can be fragile and very susceptible both to scratching by mechanical cleaning devices, and to etching by cleaning chemicals.